I am helping a friend out who has made quite a mess of his windows PC. Problem is that thar are lots of viruses, maybe rootkits and the like, I'm not a specialist.

A google redirect among other things, and It's almost impossible to get the whole disk clean... (antivirus and antispyware are interrupted constantly). I did try RKill without much succes and now wanted to try stuff like Hijack this...

But isn't it an option to scan the disk on another computer, where it isn't the startup disk anymore?

I guess that not all stuff (like the registry) can be cleaned properly than, but that isn't maybe that much of a problem.

But is there any serious danger involved? Like making the disk not boot anymore?

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3

Nuke it from Orbit, it's the only way to be sure. Then restore from backup. Also, registry hives can easily be loaded on another computer; there's nothing magical about a Windows install.
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Chris SNov 2 '11 at 12:37

The best option is to reformat the computer. You can never be sure that something is still hidden on the computer if you don't; there is the possibility that there's malware not yet found in signature databases, so if you miss it, it'll continue to download other malware or allow remote access.

You might not infect your computer in trying to get it cleaned by booting it as a non-boot disk, but you'll not actually have proof that it's cleaned either.

Also you risk having damaged libraries or files from the "cleaning" process. The computer might run, but it might also act kind of strange with lockups and crashes due to a damaged library.

Again. Nuke the drive from orbit. If you're VERY careful you can pull DATA ONLY files from the computer and scan those for malware (word/excel files, things of that nature.) Otherwise reinstall from known-good install media and start over again.

+1 I guess, but not a message I'm looking forward to bringing..
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PeterNov 2 '11 at 12:45

2

Helping non-tech people with their computers often entails bad news if you repair it responsibly. This is soon followed by blame when the computer fails for unrelated reasons and you touched it three months ago.
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Bart SilverstrimNov 2 '11 at 12:51

Yes this is an option. You can also create a boot disk, such as UBCD4Win, from a clean computer. It comes with several Antivirus and Malware programs. From the sound of it, it may be better in the long run to move off all of her data files and pictures (plus scanning them), reinstall Windows, and then reload her data, pictures, etc.